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cycle (day length). This provides a mechanism for organisms to respond to seasonal changes in the relative length of day and night. Day length changes with the seasons; the farther from the equator, the greater the variation. Flowering responses of plants to day length fall into several basic categories. When the dayl...
permits plants to flower when abiotic environmental conditions are optimal, pollinators are available, and competition for resources with other plants may be less. For example, the spring ephemerals flower in the woods before the canopy leafs out, blocking sunlight necessary for photosynthesis. At middle latitudes, mo...
iod in greenhouses ensures that short-day poinsettias flower in time for the winter holidays. Note that the colorful “petals” are actually sepals. Even after flowering is induced, there are many developmental events leading to the production of species-specific flowers. The Flowering Hormone: Does It Exist? The Holy Gr...
becoming a floral meristem by either activating or repressing the inhibition of floral meristem identity genes (figure 41.32). Two of the key floral meristem identity genes are LEAFY and APETALA1. These genes establish the meristem as a flower meristem. They then turn on floral organ identity genes. The floral organ i...
for the initiation of integuments and also those responsible for the formation of the integument have been identified. Some also affect leaf structure. This chapter has focused on the complex and elegant process that gives rise to the reproductive structure called the flower. It is indeed a metamorphosis, but the subt...
section of –C mutant flower FIGURE 41.33 ABC model for floral organ specification. Letters labeling whorls indicate which gene classes are active. When A function is lost (-A), C expands to the first and second whorls. When B function is lost (-B), both outer two whorls have just A function, and both inner two whorls h...
or, in some instances, intense light, an electrical signal is generated. The electrical signal is translated into a chemical signal, with potassium ions, followed by water, migrating from the cells in one half of a pulvinus to the intercellular spaces in the other half. The loss of turgor in half of the pulvinus cause...
become more or less vertical at night as the pulvini lose turgor (figure 41.35). These sleep movements reduce water loss from transpiration during the night, but maximize photosynthetic surface area during the day. In these cases, the movement is closely tied to an internal rhythm. Circadian Clocks How do leaves know ...
second in evolutionary time. In chapter 38, we discussed surface barriers the plant constructs to block invasion. In this section, we will focus on cellular level responses to attacks by microbes and animals. Recognizing the Invader Half a century ago, Flor proposed that there is a plant resistance gene (R) whose prod...
, defense responses are also triggered. Mechanical damage causes responses that have some similar components, but the reaction may be slower. Biochemically, it is distinct from some of the events triggered by signals in the insect’s mouth. Such responses are collectively called wound responses. Wound responses are a ch...
periods of drought. 1. In general, which part of a plant is positively phototropic? What is the adaptive significance of this reaction? • Photoperiod • Hormones • Student Research: Plant Growth • Student Research: Selection in Flowering Plants 41.2 The hormones that guide growth are keyed to the environment. • Auxin m...
its leaves are touched? 8. In what ways can a plant protect itself from pathogenic microbes? From animals? 836 Part XI Plant Growth and Reproduction 42 Plant Reproduction Concept Outline 42.1 Angiosperms have been incredibly successful, in part, because of their reproductive strategies. Rise of the Flowering Plants. A...
clonally propagate individuals. An unusual twist to sexual reproduction in some flowering plants is that senescence and death of the parent plant follows. 837 42.1 Angiosperms have been incredibly successful, in part, because of their reproductive strategies. Rise of the Flowering Plants Most of the plants we see dail...
example, there are only about 750 extant gymnosperm species! Why Are the Angiosperms Successful? When flowering plants originated, Africa and South America were still connected to each other, as well as to Antarctica and India, and, via Antarctica, to Australia and New Zealand (figure 42.3). These landmasses formed th...
, India, Australia, and Antarctica were all connected and part of the huge continent of Gondwanaland, which eventually separated into the discrete landmasses we have today. most common. Angiosperms arose in temperate and tropical terrestrial communities in a relatively short time. At about the time that angiosperms bec...
with pollinators and the result is much more complex and diverse than the initiation of four distinct whorls of organs described in chapter 40. Characteristics of Floral Evolution The evolution of the angiosperms is a focus of chapter 37. Here we need to keep in mind that the diversity of angiosperms is partly due to ...
all the female parts of a flower. In most flowers, the gynoecium, which is unique to angiosperms, consists of a single carpel or two or more fused carpels. Single or fused carpels are often referred to as the simple or compound pistils, respectively. Most flowers with which we are familiar—for example, those of tomato...
sepals, petals, stamens, carpels, or various combinations of these structures. Modifications often relate to pollination mechanisms and, in some cases like the grasses, wind has replaced animals for pollen dispersal. While much floral diversity is the result of natural selection related to pollination, it is important...
the orchid family (Orchidaceae), are bilaterally symmetrical. (a) (b) FIGURE 42.7 Genetic regulation of asymmetry in flowers. (left) Snapdragon flowers normally have bilateral symmetry. (right) The cyclodia gene regulates floral symmetry, and cyclodia mutant snapdragons have radially symmetrical flowers. The first ang...
ule Megaspore mother cell (2n) Megaspores (n) Surviving megaspore Antipodals Meiosis Polar nuclei Mitosis Synergids Egg cell Degenerated megaspores 8-nucleate embryo sac (megagametophyte) (n) FIGURE 42.8 Formation of pollen grains and the embryo sac. Diploid (2n) microspore mother cells are housed in the anther and div...
megaspores. In most plants, only one of these megaspores, however, survives; the rest are absorbed by the ovule. The lone remaining megaspore undergoes repeated mitotic divisions to produce eight haploid nuclei that are enclosed within a seven-celled embryo sac. Within the embryo sac, the eight nuclei are arranged in ...
spreading of pollen from plant to plant by pollinators visiting flowers of specific angiosperm species has played an important role in the evolutionary success of the group. It now seems clear that the earliest angiosperms, and perhaps their ancestors also, were insect-pollinated, and the coevolution of insects and pl...
of a given group of plants almost exclusively as sources of their larval food. The highly constant relationships of such bees with those flowers may lead to modifications, over time, in both the flowers and the bees. For example, the time of day when the flowers open may correlate with the time when the bees appear; t...
us, but highly visible to bees and other insects (figure 42.13). These markings can be in the form of a bull’s-eye or a landing strip. Red does not stand out as a distinct color to most insects, but it is a very conspicuous color to birds. To most insects, the red upper leaves of poinsettias look just like the other l...
normal light and (b) with a filter that selectively transmits ultraviolet light. The outer sections of the petals reflect both yellow and ultraviolet, a mixture of colors called “bee’s purple”; the inner portions of the petals reflect yellow only and therefore appear dark in the photograph that emphasizes ultraviolet ...
numbers of ill-adapted individuals because it brings together deleterious recessive genes; but some of these combinations may be highly advantageous in particular habitats. In such habitats, it may be advantageous for the plant to continue self-pollinating indefinitely. This is the main reason many self-pollinating pl...
a particular plant species, these organs may reach maturity at different times. Plants in which this occurs are called dichogamous. If the stamens mature first, shedding their pollen before the stigmas are receptive, the flower is effectively staminate at that time. Once the stamens have finished shedding pollen, the ...
as illustrated by the flowers of fireweed, Epilobium angustifolium. More than 200 years ago (in the 1790s) fireweed, which is outcrossing, was one of the first plant species to have its process of pollination described. First, the anthers shed pollen, and then the style elongates above the stamens while the four lobes...
atibility (b) Sporophytic self-incompatibility Chapter 42 Plant Reproduction 847 Fertilization Fertilization in angiosperms is a complex, somewhat unusual process in which two sperm cells are utilized in a unique process called double fertilization. Double fertilization results in two key developments: (1) the fertiliz...
stigma of a flower, the pollen tube cell grows toward the embryo sac, forming a pollen tube. While the pollen tube is growing, the generative cell divides to form two sperm cells. When the pollen tube reaches the embryo sac, it bursts through one of the synergids and releases the sperm cells. In a process called doubl...
izomes specialized for storage and reproduction. White potatoes are propagated artificially from tuber segments, each with one or more “eyes.” The eyes, or “seed pieces,” of potato give rise to the new plant. Suckers. The roots of some plants—for example, cherry, apple, raspberry, and blackberry—produce “suckers,” or s...
, than in temperate regions. Plants that reproduce asexually clone new individuals from portions of the root, stem, leaves, or ovules of adult individuals. The asexually produced progeny are genetically identical to the parent individual. Chapter 42 Plant Reproduction 849 42.4 How long do plants and plant organs live? ...
die after flowering once, the developing flowers or embryos using hormonal signaling to reallocate nutrients so the parent plant literally starves to death. This can be demonstrated by comparing a population of bean plants where the beans are continually picked with a population where the beans are left on the plant. ...
. In northern temperate regions, conifers are the most familiar evergreens; but in tropical and subtropical regions, most angiosperms are evergreen, except where there is a severe seasonal drought. In these areas, many angiosperms are deciduous, losing their leaves during the drought and thus conserving water. Organ Ab...
protective layer FIGURE 42.21 Leaf abscission. The abscission zone of a leaf. Hormonal changes in this zone cause abscission. Two layers of cells in the abscission zone differentiate into a protective layer and a separation layer. As pectins in the separation layer break down, wind and rain can easily separate the lea...
What flower whorl is collectively made up of petals? With which other flower parts are the petals of most flowers homologous? 3. What is an androecium? Of which flower parts is it composed? 42.2 Flowering plants use animals or wind to transfer pollen between flowers. • Bees are the most frequent and constant pollinato...
As agrarian societies formed, people began to select for desirable traits. Until relatively recently, plant biologists focused their research efforts on variation in chromosomes, but work is now shifting increasingly to the molecular level. Organization of Plant Genomes. Plant genomes are more complex than those of ot...
. This chapter looks ahead to the impact of these new technologies on the future of plants and our study of plant biology (figure 43.1). Both the Arabidopsis and rice genomes are essentially sequenced. Not only can we expect to learn much about the molecular basis of plant physiology and development from these rich dat...
otide base-pairs) exhibits the greatest variation of any kingdom in the biological world. For example, tulips contain over 170 times as much DNA as the small weed Arabidopsis thaliana (table 43.1). The DNA of plants, like animals, can also contain 854 Part XI Plant Growth and Reproduction Haploid Diploid Polyploid FIGU...
B Triticum tauschii (2n =14) CC Sterile hybrid(1n =21) ABC Chromosome doubling Triticum aestivum (2n =42) AABBCC Hexaploid: 67 FIGURE 43.3 Evolutionary history of wheat. Domestic wheat arose in southwestern Asia in the hilly country of what is now Iraq. In this region, there is a rich assembly of grasses of the genus T...
genomes in several different arrangements. The arrows represent repeated DNA sequences. Arrows of the same size and color represent DNA sequences which are identical to each other. The direction of the arrowhead indicates the orientation of the DNA sequence. (b) Transposable elements can be a source of repetitive DNA ...
”). In addition, groups of repetitive DNA sequences can also occur together in plant genomes in a variety of possible arrangements, such as a “compound tandem array” or a “repeat/repeat interspersion.” The presence of repetitive DNA can vastly increase the size of a plant genome, making it difficult to find and charact...
plant cell by endosymbiosis. In support of this concept, research has shown that chloroplast DNA has many prokaryote-like features. Chloroplast DNA is present as circular loops of double-stranded DNA similar to prokaryotic chromosomal DNA. Moreover, chloroplast DNA contains genes for ribosomes that are very similar to...
ology, there is increasing use of plant molecular data such as chloroplast DNA sequences. When considered together, morphological and molecular information can provide a clearer understanding of the evolutionary processes that govern biological diversity. Plant nuclear genomes may contain large amounts of DNA in compar...
restriction enzymes that cleave at specific sites. RFLP mapping can identify important regions of the genome at a glance, while sequence data require sophisticated computer-based searching and matching systems. A comparison of the RFLP maps of parents and progeny can give an indication of the heritability of gene trai...
probe 2 Mix Hybridize Strong signal from probe 1 Weak signal from probe 1 4. The two probes are mixed and hybridized with the microarray. Fluorescent signals on the microarray are analyzed. FIGURE 43.7 Microarrays. Microarrays are created by robotically placing DNA onto a microscope slide. The microarray can then be p...
tenacity to apply new sequencing technology to an entire genome, rather than single genes. Powerful databases are being constructed to make this information accessible to all. The completely sequenced Arabidopsis genome will have far-reaching uses in agricultural breeding and evolutionary analysis. This information ca...
technology. Research will move from genomics to proteomics (the study of all proteins in an organism). Proteins are much more difficult to study because of posttranslational modification and formation of complexes of proteins. This information will be essential in understanding cell biology, physiology, development, a...
in chapter 19 and below, desirable genes can be introduced into plants, yielding transgenic cells and tissues. Whole plants can than be regenerated using tissue culture. While animals can now be cloned, the process is much simpler in plants. Many somatic (not germ-line) plant cells are totipotent, which means they can...
anced media, and roots and shoots begin to form. (c) The plantlets are then separated and grown to maturity. Types of Plant Tissue Cultures Depending on the type of plant tissue used as the explant and the composition of the growth medium, a variety of different types of plant tissue cultures can be generated. These di...
applications where access to single cells is important. The suspension bath can provide an efficient means for selecting out cells with desirable traits such as herbicide tolerance or salt tolerance because the bath is in uniform contact with all the cells at once. This differs from callus culture, where only those ce...
plants. Plant protoplasts are also more easily transformed with foreign DNA using approaches such as electroporation (see the subsequent section). In addition, protoplasts isolated from different plants can be forced to fuse together to form a hybrid. If they are regenerated into whole plants, these hybrids formed fro...
Chromosome duplication results in the conversion of sterile haploid plants into fertile diploid organisms. Under these conditions, plants can be produced that are homozygous for every single trait, even those which tend to be recessive traits. On a cautionary note, not every cell exposed to colchicine becomes diploid....
icrobial compounds, antitumor alkaloids, vitamins, insecticides, and food flavors. Plant roots can also be grown in liquid culture, creating a mesh of roots that can produce a number of useful plant compounds. Horticultural Uses Plants with valuable traits can be mass propagated through tissue-culture cloning. In this ...
or following the regeneration of whole plants by either organogenesis or embryogenesis (plant size, photosynthetic rates, and so forth). Plant cell, tissue, and organ cultures have important applications in agriculture and industry. Chapter 43 Plant Genomics 867 43.3 Plant biotechnology now affects every aspect of agr...
Plant Growth and Reproduction Plant Biotechnology for Agricultural Improvement It seems certain that plant genetic engineering will play a major role in resolving the problem of feeding an increasing world population. The nutritional quality of crop plants is being improved by increasing the levels of nutrients they c...
modify seed oil biochemistry to produce “designer oils” for edible and nonedible products. One technique modifies canola oil to replace cocoa butter as a source of saturated fatty acids; others modify the enzyme ACP desaturase for the creation of monounsaturated fatty acids in transgenic plants. High-lauric acid canol...
keep the traditional vaccine cold (remember that proteins degrade rapidly as the temperature increases). Genetic engineering of crop plants has allowed researchers to alter the oil content, amino acid composition, and vitamin content of food crops. Genetic engineering may also allow the production of food crops bearin...
play an important role in the further improvement of crop plants. The particle gun and electroporation are useful methods for introducing foreign DNA into plants. 870 Part XI Plant Growth and Reproduction HV(+) HV(–) Discharge chamber DNA coated gold particles on film Retaining screen Target cells/tissue (a) – + DNA C...
mainly due to a high amount of repetitive DNA. • Plant genomes can be compared with one another by mapping the locations of certain genes or gene traits in various plants. RFLPs and AFLPs can be used to map plant DNA. • Arabidopsis thaliana has a small genome, for a plant. This complete genome is essentially sequenced...
cells. This can be achieved using a particle gun or electroporation. 7. Describe how the particle gun and electroporation can be used to introduce foreign DNA into plant cells. Which approach requires the use of plant protoplasts? Why? 8. How can a plant be “engineered” to produce an edible vaccine? 872 Part XI Plant ...
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. Some of the earliest invertebrates to evolve, marine flatworms possess internal organs but lack a true cavity called a coelom. We will now explore the great diversity of animals, the result of a long evolutionary history. Animals, constituting millions of species, are among the most abundant living things. Found in e...
. The cells of all animals but sponges are organized into structural and functional units called tissues, collections of cells that have joined together and are specialized to perform a specific function; muscles and nerves are tissues types, for example. Active Movement. The ability of animals to move more rapidly and...
shape and symmetry and, in most cases, tissues organized into organs and organ systems. Although very different in structure, both types evolved from a common ancestral form (figure 44.2) and possess the most fundamental animal traits. All eumetazoans form distinct embryonic layers during development that differentiat...
Noncoelomate Animals 877 Table 44.1 The Major Animal Phyla Phylum Typical Examples Key Characteristics Arthropoda (arthropods) Beetles, other insects, crabs, spiders Most successful of all animal phyla; chitinous exoskeleton covering segmented bodies with paired, jointed appendages; many insect groups have wings Appro...
than 30,000 species known as fossils Ctenophora (sea walnuts) Comb jellies, sea walnuts Gelatinous, almost transparent, often bioluminescent marine animals; eight bands of cilia; largest animals that use cilia for locomotion; complete digestive tract with anal pore Phoronida (phoronids) Phoronis Lophophorate tube worm...
3b). A bilaterally symmetrical body plan has a top and a bottom, better known respectively as the dorsal and ventral portions of the body. It also has a front, or anterior end, and a back, or posterior end. In some higher animals like echinoderms (starfish), the adults are radially symmetrical, but even in them the lar...
evolution of efficient organ systems within the animal body was not possible until a body cavity evolved for supporting organs, distributing materials, and fostering complex developmental interactions. Ectoderm Mesoderm Ectoderm Mesoderm Visceral peritoneum Coelomic cavity Endoderm Parietal peritoneum Ectoderm Mesoder...
(figure 44.4). The development of the coelom poses a problem—circulation—solved in pseudocoelomates by churning the fluid within the body cavity. In coelomates, the gut is again surrounded by tissue that presents a barrier to diffusion, just as it was in solid worms. This problem is solved among coelomates by the deve...
a, Echinodermata (starfish) and Chordata (vertebrates), together with two smaller phyla, have a series of key embryological features different from those shared by the other animal phyla. Because it is extremely unlikely that these features evolved more than once, it is believed that these four phyla share a common anc...
individual segments can move independently because the animal as a whole has more flexibility of movement. Because the separations isolate each segment into an individual skeletal unit, each is able to contract or expand autonomously in response to changes in hydrostatic pressure. Therefore, a long body can move in wa...
, no more than a few millimeters across, some, like the loggerhead sponges, may reach 2 meters or more in diameter. A few small ones are radially symmetrical, but most members of this phylum completely lack symmetry. Many sponges are colonial. Some have a low and encrusting form, while others may be erect and lobed, so...
of fidelity and are specialized for different functions of the body. The basic structure of a sponge can best be understood by examining the form of a young individual. A small, anatomically simple sponge first attaches to a substrate and then grows into a vaselike shape. The walls of the “vase” have three functional ...
beats its flagellum, water is drawn down through openings in its collar, where food particles become trapped. The particles are then devoured by endocytosis. FIGURE 44.7 The body of a sponge is multicellular. The first evolutionary advance seen in animals is complex multicellularity, in which individuals are composed ...
-ree-ah), the cnidarians—hydroids, jellyfish, sea anemones, corals—and and Ctenophora (pronounced tea-NO-forah), the comb jellies, or ctenophores. All other eumetazoans are in the Bilateria and exhibit a fundamental bilateral symmetry. The Cnidarians Gastrovascular cavity Epidermis Mesoglea Gastrodermis Tentacles Medus...
in composition. They differ markedly from the sponges in organization; their bodies are made up of distinct tissues, although they have not evolved true organs. These animals are carnivores. For the most part, they do not actively move from place to place, but rather capture their prey (which includes fishes, crustace...
st Hydra Hydra and jellyfish are carnivores that capture their prey with tentacles that ring their mouth. Cross-section Stinging cell (cnidocyte) with nematocyst Trigger Undischarged nematocyst Filament The barb explodes out of the stinging cell at a high velocity and can even penetrate the hard shell of a crustacean. ...
fish contains a number of specialized epitheliomuscular cells, each of which can contract individually. Together, the cells form a muscular ring around the margin of the bell that pulses rhythmically and propels the animal through the water. Jellyfish have separate male and female individuals. After fertilization, plan...
medusa stage is dominant—much larger and more complex than the polyps. The medusae are bell- 888 Part XII Animal Diversity Class Cubozoa: The Box Jellyfish. Until recently the cubozoa were considered an order of Scyphozoa. As their name implies, they are boxshaped medusa (the polyp stage is inconspicuous and in many c...
als help form coral reefs, which are shallow-water limestone ridges that occur in warm seas. Although the waters where coral reefs develop are often nutrient-poor, the coral animals are able to grow actively because of the abundant algae found within them. The Ctenophorans (Comb Jellies) The members of this small phylu...
oderm, and mesoderm. We will focus our discussion of the acoelomates on the largest phylum of the group, the flatworms. Phylum Platyhelminthes: The Flatworms many other kinds of animals (figure 44.16). Other flatworms are free-living, occurring in a wide variety of marine and freshwater habitats, as well as moist place...
Part XII Animal Diversity PHYLUM PLATYHELMINTHES: Bilateral symmetry Solid worms are bilaterally symmetrical acoelomates. Their bodies are composed of solid layers of tissues surrounding a central gut. The body of many flatworms is soft and flattened, like a piece of tape or ribbon. Hooks Scolex attached to intestinal...
worms have thin bodies and highly branched digestive cavities that make such a relationship possible. The nervous system of flatworms is very simple. Like cnidarians, some primitive flatworms have only a nerve net. However, most members of this phylum have longitudinal nerve cords that constitute a simple central nervo...
Egg containing miracidium Miracidium hatches after being eaten by snail Redia Sporocyst FIGURE 44.17 Life cycle of the human liver fluke, Clonorchis sinensis. Flukes take in food through their mouth, just like their free-living relatives. There are more than 10,000 named species, ranging in length from less than 1 mil...
Other very important flukes are the blood flukes of genus Schistosoma. They afflict about 1 in 20 of the world’s population, more than 200 million people throughout tropical Asia, Africa, Latin America, and the Middle East. Three species of Schistosoma cause the disease called schistosomiasis, or bilharzia. Some 800,0...
. Embryos, each surrounded by a shell, emerge from the proglottid through a pore or the ruptured body wall. They are deposited on leaves, in water, or in other places where they may be picked up by another animal. The beef tapeworm Taenia saginata occurs as a juvenile in the intermuscular tissue of cattle but as an adu...
ribbon worm, Lineus ( phylum Nemertea). This is the simplest animal with a complete digestive system. Chapter 44 The Noncoelomate Animals 893 44.4 Pseudocoelomates have a simple body cavity. The Pseudocoelomates All bilaterians except solid worms possess an internal body cavity, the third key transition in the animal ...
It is the only animal whose complete developmental cellular anatomy is known. About 50 species of nematodes, including several that are rather common in the United States, regularly parasitize human beings. The most serious common nematode-caused disease in temperate regions is trichinosis, caused by worms of the genu...
, less than a millimeter long— hundreds of thousands may live in a handful of fertile soil. An adult nematode consists of very few cells. Caenorhabditis elegans has exactly 959 cells and is the only animal whose complete cellular anatomy is known. Intestine Pseudocoel Oviduct Cuticle The pseudocoel of a nematode separa...
they are beating together, resemble the movement of spokes radiating from a wheel. In December 1995, two Danish biologists reported the discovery of a strange new kind of creature, smaller than a period on a printed page. The tiny organism had a striking circular mouth surrounded by a ring of fine, hairlike cilia and ...
, leaving them, for example, with no body cavity (they are acoelomates) and only incomplete segmentation. This character loss has led to considerable disagreement among taxonomists. However, while taxonomists have disagreed about the details, all have generally allied myzostomids is some fashion with the annelids, some...
Molecular phylogenies developed from different molecules often tend to suggest different evolutionary relationships. However, the childhood of this approach is likely to be short. Over the next few years, a mountain of additional molecular data can be anticipated. As more data are brought to bear, we can hope that the...
. • Animals are heterotrophic, multicellular, and usually have the ability to move. Almost all animals reproduce sexually. Animal cells lack rigid cell walls and digest their food internally. • The kingdom Animalia is divided into two subkingdoms: Parazoa, which includes only the asymmetrical phylum Porifera, and Eumet...
eworms different from flukes? How do tapeworms reproduce? • Bilateral Acoelomates • Student Research: Parasitic Flatworms • Pseudocoelomates, exemplified by the nematodes (phylum Nematoda), have a body cavity that develops between the mesoderm and the endoderm. • Rotifers (phylum Rotifera), or wheel animals, are very s...
Lophophorates. The three phyla of lophophorates share a unique ciliated feeding structure, but differ in many other ways. FIGURE 45.1 An annelid, the Christmas-tree worm, Spirobranchus giganteus. Mollusks and annelids inhabit both terrestrial and aquatic habitats. They are large and successful groups, with some of the...
collect, preserve, and study. Chitons and nudibranchs are less familiar marine mollusks. Mollusks are characterized by a coelom, and while there is extraordinary diversity in this phylum, many of the basic components of the mollusk body plan can be seen in figure 45.3 As a group, mollusks are an important source of fo...
long as 1.5 meters and may weigh as much as 270 kilograms. Mollusks are the second-largest phylum of animals in terms of named species; mollusks exhibit a variety of body forms and live in many different environments. Mollusks evolved in the oceans, and most groups have remained there. Marine mollusks are widespread a...
completely enclosed within the mesoderm. This allows physical contact between the mesoderm and the endoderm, permitting interactions that lead to development of highly specialized organs such as a stomach. FIGURE 45.4 Giant clam. Second only to the arthropods in number of described species, members of the phylum Mollu...
layer of bivalve mollusks (two-shelled), including clams and oysters. The mantle coats the foreign object with layer upon layer of shell material to reduce irritation caused by the object. The shell of mollusks serves primarily for protection. Many species can withdraw for protection into their shell if they have one....